Photoconductivity of Cu x Ag1−x Cd2InTe4

Summary The prominent photoelectric parameters of the semiconducting solid solutions Cu _x Ag_1−x Cd₂InTe₄ are reported. From the spectral dependence of photoconductivity at room temperature and at 77 K the energy gaps and their thermal coefficients are obtained. The detectivityD ^*, the photocurrent gainG and the carrier lifetime are measured and the carrier mobility is deduced. In order to improve theD ^* characteristics, the analysis of its parameters is also performed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

An optimization model for amorphous solar cells in which optical,electrical and recombination properties are specified

Summary A model for determination and optimization of the fundamental parameters defining the quality of amorphous solar cells in which optical, electrical and recombination properties are specified is developed. It can be applied to any amorphous solar-cell systems. This paper gives theoretical expressions and describes an iterative method of numerical calculation for the current density of different cells. Results of computer calculations based on this model are presented.

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Riassunto In questo lavoro si presenta un modello per la determinazione e l'ottimizzazione dei parametri fondamentali atti a definire la qualità delle celle solari amorfe, specificando le proprietà ottiche, elettriche e di ricombinazione. Esso può essere applicato a qualunque sistema di celle solari amorfe. Sono fornite le espressioni teoriche ed è descritto un metodo iterativo per il calcolo numerico della densità di corrente di alcuni tipi di celle. Sono anche presentati i risultati ottenuti da calcoli eseguiti col computer e basati su questo modello.

     

High-T c Josephson junctions for electronic applications

Summary The current status of the electronic applications of high-T _c Josephson junctions is briefly reviewed. Recent results obtained by the authors on devices employing step-edge junctions are reported. In particular the design of a microwave oscillator based on a parallel array of junctions is discussed and preliminary experimental results are presented. Paper presented at the ?VII Congresso SATT? Torino, 4–7 October 1994.     

BCS quasi-particle tunnelling current in Josephson tunnel junctions

Summary The recent improvements in the fabrication technology have succeeded in obtaining high-quality Josephson tunnel junctions. TheI–V characteristics of these junctions exhibit now lesser and lesser differences from the theoretical predictions. The various figures of merit, so far introduced to qualify the junctions, appear now focused on too limited aspects and a direct comparison with the detailed prediction of the theory is in order. For this awaken interest in the detailed predictions of the BCS theory, we have revisited the relevant formulae for the quasi-particle tunnelling current. A detailed discussion of the analytical transformation necessary for a simple numerical evaluation of this current is reported. SeveralI–V curves are obtained using the parameter values corresponding to the case of Nb-based junctions, which is the actual running technology. Peculiar interesting aspects are outlined.     

Anomalies and proximity effect in high-T C tunnel junctions

Summary Some of the main anomalies in conductance characteristics of high-T _C tunnel junctions are considered. Mainly, the extreme, depression of gap structures, the presence of conductance peaks in corrispondence to the counterelectrode gap, and ?zero-bias anomalies? will be examined. The possibility of application of the proximity McMillan model to describe the behaviour in conductance of high-T _C junctions is considered. Discussion and preliminary comparison with experimental data on YBCO junctions are also reported.     

Generation of subharmonic shapiro steps in ladder arrays of overdamped superconducting junctions

Summary Subharmonic Shapiro Steps (SSS) are usually observed in 2D arrays of superconducting junctions when their dynamical states are perturbed by factors like disorder, frustration, current inhomogeneities and so on. In order to clarify the conditions under which SSS can be generated we decided to investigate arrays of very simple shape like the ladder ones. In particular we have studied the influence of the frustration (i.e. of an external magnetic field) on the time evolution of the vortex configuration and the commensurability of the latter with the geometry and the dimension of the array. Ladders, parallel or perpendicular to the bias current, turn out to be systems where the properties of the square arrays can be suitably tested. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.     

Diastereofacial selectivity in some 4‐substituted (X) 2‐adamantyl derivatives: electronic versus steric effects

π‐Facial selectivity data for the reduction and methylation of some 4^ax‐substituted (X) 2‐adamantanones ( 3 , Y = O) as well as the nucleophilic trapping of secondary and tertiary 4^ax‐substituted (X)‐2‐adamantyl cations ( 4 ; R = H and CH₃, respectively) and the 4‐methylene‐2‐adamantyl radical ( 8 ) are presented. The pronounced anti‐face selectivities observed for ( 3 , Y = O and 4 , R = CH₃) emphasize the importance of the steric factor as expected for systems with a strong steric bias. However, the dominant syn‐face capture of 4 (R = H) was completely unexpected and highlights a subtle interplay between steric and electronic effects. Finally, the very high anti‐face stereoselectivity for the trapping of ( 8 ) with the trimethylstannyl anion (Me₃Sn^?) is rationalized in terms of an electrostatic effect overwhelming the steric factor. Copyright © 2007 John Wiley & Sons, Ltd.     

Electric field-induced stress birefringence in layered composites PbZr1-xTixO3/Polycarbonate

Electro-optical composites based on the product of electro-strictive and elasto-optical effects are developed.Layered composites of PbZr 1 x Ti x O 3 and polycarbonate are synthesised.Their electro-optical properties are studied.The nominal transverse electro-optical coefficient of the composite is observed to be about 3.6 times larger than that of LiNbO 3.Experiments and theoretical analyses show that the electro-optical effect of the composite has a strong ’size effect’.With the ratio of thickness/length decreasing or the width of elasto-optical phase increasing,the half-wave electric field intensity increases but the transverse electro-optical coefficient decreases for the layered composite.     

Quantum theory of high-electric-field magnetotransport for a two-dimensional electron gas in microstructures

Summary Nonlinear response to an electric field applied in the plane of a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field is expressed in terms of an electric-field (F)-dependent magnetoconductivity in which the effect of the electric field is incorporated in the resolvent of the Liouville operator. This electric-field-dependent Kubo-type formula is calculated in the presence of the simultaneous scattering by disorder and phonons and is expressed in terms of the electric-field-dependent broadening and shifting of the Landau levels. It is found to be essential to treat the two interactions simultaneously and self-consistently at low temperatures. High-field effects such as ?collisional broadening? and ?intracollisional field effects? as manifested through the electric-field-dependent tetradic self-energy of 2DEG in a perpendicular magnetic field are calculated and shown to be much more pronounced in 2DEG as compared to the same phenomenon in three-dimensional semiconductors. The present results are found to be useful in the calculation of the effects of the temperature (T), magnetic field (B) and the electric field (F) as well as the interplay of the two interactions on the quantum effects as manifested in the Landau level broadening due to the relaxation and acceleration of the electrons in an applied electric field. In the limitF→0 the present results reduce to the usual formulae as known from the linear response theory.     

High-quality YBCO d.c. SQUIDs based on bicrystal substrates

Summary An analysis of superconducting transport properties and magnetic behaviour of d.c. SQUIDs employing YBCO bicrystal grain boundary junctions (GBJs) has been performed. GBJs have been obtained by deposition of ac-axis-oriented YBCO film on a SrTiO₃ bicrystal substrate by ICM sputtering technique. Experimental measurements on a YBCO d.c. SQUID with a misorientation angle θ=20° are reported. The SQUID shows a critical temperatureT _c∼89 K and a high critical current densityJ _c∼3·10⁶ A/cm² atT=4.2 K. Current-voltage characteristics are close to the behaviour predicted by the resistively shunted junction (RSJ) model and the temperature dependenceJ _c(T) shows a linear behaviour at small reduced temperatures and a depressedJ _c value close toT _c. High-quality flux-voltage curves have been found upT=87 K over a large range of magnetic field. The high reproducibility and the good control of transport properties by the variation of θ make YBCO bicrystal GBJs very useful for applications in electronics. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.     

The influence of steric effects on the kinetics and mechanism of SNAr reactions of 1‐phenoxy‐nitrobenzenes with aliphatic primary amines in acetonitrile

Rate constants are reported for the reactions of 1‐phenoxy‐dinitrobenzenes, 3 , 1‐phenoxy‐dinitrotrifluoromethylbenzenes, 4 , with n‐propylamine, and 1‐methylheptylamine in acetonitrile as solvent. The results are compared with results reported previously for n‐butylamine, pyrrolidine, and piperidine. Decreasing ring activation leads to lower values of k₁ for nucleophilic attack although this may be mediated by reduced steric congestion around the reaction centre. Specific steric effects, leading to rate retardation, are noted for the ortho‐CF₃ group. In general, reactant‐bearing ortho‐CF₃ group were subject to base catalysis irrespective of the amine nucleophile and values of k_Am/k_?1 are reduced as the size of the amine get bulkier. This is likely to reflect increases in values of k_?1 coupled with decreases in values of k_Am as the proton transfer from zwitterionic intermediates to catalysing amine becomes less thermodynamically favourable.     

Coordinate space form of interacting reference response function ofd-dimensional jellium

Summary The interacting reference response functionX _I ^[3](k) of three-dimensional jellium ink space was defined by Niklasson in terms of the momentum distribution of the interacting electron assembly. Here the Fourier transformF _I ^[d](r) ofX _I ^[d] (k) is studied for the jellium model withe ²/r interactions in dimensionalityd=1,2 and 3, in an extension of recent work by Holas, March and Tosi for the cased=3. The small-r and large-r forms ofF _I ^[d] (r) are explicitly evaluated from the analytic behaviour of the momentum distributionn _d(p). In the appendix, a model ofn _d (p) is constructed which interpolates between these limits.     

Balance equations for electron transport in an arbitrary energy band driven by an intense terahertz field. Application to superlattice miniband transport

We suggest a balance-equation approach to hot-electron transport in a single arbitrary energy band subject to an intense radiation field of terahertz (THz) frequency, including all the multiphoton emission and absorption processes and taking account of realistic scatterings due to impurities and phonons. This approach, which allows one to calculate THz-driving, time-averaging transport based on a set of time-independent equations, provides a convenient method to study the effect of an intense THz electric field on carrier transport in a nonparabolic energy band. As an example, these fully three-dimensional, acceleration- and energy-balance equations are applied to the discussion of superlattice miniband transport at lattice temperature T=77 and 300 K driven by the THz radiation field of varying strengths. It is shown that the current through a dc biased miniband superlattice is greatly reduced by the irradiation of an intense THz electric field. Received: 23 January 1998 / Revised: 31 March 1998 / Accepted: 20 April 1998     

Temperature dependence of the superconducting energy gap from conductance curves

Summary An analytic relationship between the values of the applied voltages which produce a maximum in the differential conductance and the energy gap is derived for BCS isotropic superconductors. The different methods of deduction of the temperature dependence of the gap in high-T _c superconductors are analysed.     

Water and alcohol(s): what's the difference? A proton NMR and DFT study of hetero‐association with pyridine

Hetero‐association of water and some simple aliphatic alcohols with pyridine in benzene has been studied by ¹H nuclear magnetic resonance (NMR) spectroscopy at very low donor concentration, where self‐association is negligible. Association constants for the formation of 1:1 and 2:1 pyridine:water complexes can then be determined without recourse to ad hoc computer programmes. That for association of a second pyridine with water is about 10 times lower than for the first. Reaction parameters for the first association with water are very similar to those for the alcohols, whereas the reaction enthalpy for the second association is somewhat smaller. The chemical shift of the OH protons and the H? C? O? H coupling constants for alcohols at high dilution in benzene are almost identical with gas‐phase data. The change in chemical shift upon association with pyridine correlates with the free energy of the reaction. Quantum mechanical calculations [BPE0 functional, 6‐311+G(d,p) basis set and a polarized continuum model of the solvent (IEFPCM)] have been run on complexes of pyridine with water, both 1:1 and 2:1, and with four alcohols. Calculated reaction enthalpies are in qualitative and, in some cases, almost quantitative agreement with the experimental data. The association constants for 1:1 complexation of pyridine with alcohols follow a rough Taft correlation in terms of polar substituent constants. Substituent size, even in the case of very bulky groups, seems to be unimportant. Copyright © 2008 John Wiley & Sons, Ltd.     

X-ray energy levels: Deviations between experimental and theoretical values

Energy values ofK, L _II andL _III levels calculated by the relativistic self consistent field method have been used to compute the energies ofKα _{1, 2} lines. These values deviate considerably from the experimental values due to Bearden and Burr. The deviations are discussed and given an empirical fit.     

Classical Representation of a Quantum System at Equilibrium

A quantum system at equilibrium is represented by a corresponding classical system, chosen to reproduce the thermodynamic and structural properties. The objective is to develop a means for exploiting strong coupling classical methods (e.g., MD, integral equations, DFT) to describe quantum systems. The classical system has an effective temperature, local chemical potential, and pair interaction that are defined by requiring equivalence of the grand potential and its functional derivatives with respect to the external and pair potentials for the classical and quantum systems. Practical inversion of this mapping for the classical properties is effected via the hypernetted chain approximation, leading to representations as functionals of the quantum pair correlation function. As an illustration, the parameters of the classical system are determined approximately such that ideal gas and weak coupling RPA limits are preserved (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stimulated brillouin scattering of alfvén wave in a highly collisional magnetoactive compensated semiconductor: Kinetic theory

Summary A rigorous theoretical investigation has been made on stimulated Brillouin scattering of electromagnetic Alfvén wave propagating in a highly collisional magnetoactive compensated semiconductor,viz. compensated germanium. By using the Krook-model solution, the Boltzmann transport equation has been solved to obtained the non-linear response of electrons and holes in the semiconductor sample immersed in an external static magnetic field. It is noticed here that the threshold of this parametric instability is quite low and the growth rate of it is considerably large at moderate power of the incident Alfvén wave. It is also noted that the effect of the electron-phonon collision frequency on this three-wave parametric process is remarkable and its growth rate decreases very rapidly with the electron-phonon collision frequency in the semiconductor.     

Reentrant resistance via spin-polarized quasiparticle self injection in CMR/HTSC heterostructures

Epitaxial superlattices of half-metal, colossal magnetoresistive La_2/3Ca_1/3MnO₃ (HM-CMR) and high-T_c superconducting YBa₂Cu₃O_7-δ (HTSC) are grown with thick and thin modulation lengths (Λ) of YBCO/LCMO, with Λ = 280 nm and 12.5 nm; respectively, on SrTiO₃ (0 0 1) single-crystalline substrates by pulsed laser deposition. Transport measurements R(T) show a resistive state below T = 35 K although the superconducting transition temperature is found to be T_c = 60 K and 63 K for both different superlattices, respectively. The onset of the resistive state coincides with a magnetic transition of the samples. This can be explained by a diffusion of spin-polarized quasiparticles into the superconducting film. Which can be considered as evidence for inverse-proximity effects over a wide temperature range in HM-CMR/HTSC heterostructures.     

Damage effects of γ-radiation on lipid bilayers

Summary The lipid composition of multi-lamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine exposed to¹³⁷Cs γ-rays depends on the absorbed dose. In fact,³¹P and¹H NMR analysis shows that four new molecular species are formed during the irradiation:a) 1-palmitoyl-sn-glycero-3-phosphorylcholine,b) 2-palmitoyl-sn-glycero-3-phosphorylcholine,c) glycerophosphorylcholine andd) free palmitic acid. Neglecting the speciesc), that is present only at high dose and in very small amount, the behaviour of molar fractionvs. dose is sublinear fora) andb), while ford) it is almost linear over all the dose range examined. The molecular and structural damage consequences onto the multi-lamellar vesicles, evidentiated by spin-labelling and DSC techniques, are discussed. It is clearly shown in particular, that the behaviour of the main transition does not depend on the concentration of the lysolecithins, but rather on that of the free palmitic acid, the role of which had previously been entirely neglected. The authors of this paper have agreed to not receive the proofs for correction.